Integrated or combined controls or control systems are common in the heating, ventilating and air conditioning (HVAC) industry. It is common for these types of controls to have some type of limited diagnostic capabilities, which typically result as an error code being translated as a blink code on an LED (light emitting diode), or as a display on a seven segment display. Until recently, most of these error codes were only shown while the actual error was happening, or while a lock-out condition persisted, while some controls might continue to display the fault code for a period of time after the fault condition abated. In any event, a loss of power to the control board resulted in a reset of the controls and the loss of any error information without the possibility of recall. So, when a repair technician went to evaluate a problem, because the home or business owner had usually already shut power down to the unit, the error code was no longer displayed. The service technician, upon arrival to the site, may also remove a metal panel which is often connected to a power disconnect switch. If this is done before looking through a site-glass for any applicable error codes (if a site-glass is even provided on the access door), again the potentially valuable information of the error code would be lost. Unless the error duplicates itself immediately upon test by the service technician, a lengthy trial and error period may be required to finally find and then fix the problem.
Over the last couple of years, an electrically erasable programmable read-only memory (EEPROM) and/or other non-volatile memory within a control panel has been used to store these error codes, such that they are displayable even after a power loss and control reset, or are otherwise recallable, such as through the use of an error recall mechanism. In some cases, even multiple errors are recorded in the EEPROM or other non-volatile memory, such that a history of faults can be saved and recalled. This type of error code information is extremely valuable to service technicians. Instead of an on-site service technician waiting for a problem to re-occur, or trouble shooting a broken furnace, for example, through a long process of trial and error techniques without any past history, the furnace control can direct the technician in the direction of the actual cause, and at least minimize the amount of trouble shooting required. The fault codes that are stored in memory can typically be cleared using a communications command or a switch such as a pushbutton on the control.
During production, HVAC units are typically tested after being assembled. During this process, commonly called “run testing,” certain faults may occur or may be introduced into the unit to test various functions of the unit. These faults are stored in a fault code memory of the control. Prior to releasing the product for shipment to a customer, these faults must be cleared from the control memory so that the fault code history begins with installation of the unit.
Prior art controls typically have a switch, usually a button, on the control to clear the fault code memory, requiring that a factory worker interact with the control to clear the memory. The button is typically provided for a technician to recall errors stored in the fault code memory, but when held in a depressed fashion for a period of time, also acts to reset the fault code memory. Thus, a run test operator would typically have to depress the button for a certain period of time to clear the fault code memory after testing. This time is usually relatively long (several seconds) to make sure that the service technician doesn't inadvertently clear the memory while displaying active fault codes using the button. Pressing and releasing a control switch over and over may pose ergonomic problems for the worker and creates the possibility of damage to the control by mishandling. Furthermore, the human element creates the possibility of other errors, such as those that may arise from inconsistent manipulation of the control switch and the like.
Other types of prior art controls have a communications feature that clear the fault code memory when the HVAC control receives a certain command via a communications port. While this technique overcomes some deficiencies by eliminating the human element, the use of a communications port requires that the run test station have the ability to communicate with the communications control port. It also requires that a dedicated communications connection be made with the HVAC control in addition to the typical thermostat signal inputs used for run testing. This equipment is expensive and generally atypical in HVAC unit testing environments. Furthermore, making the communications connection to the control requires additional time, which slows production.
Accordingly, what is needed is a method for clearing an HVAC control fault code memory that overcomes these and other problems found in prior art systems.